In the paper, we identify a problem for certain applications wishing to use the Web service paradigm to enhance interoperability: rapid, robust state maintenance. While many features are available to support session data, special mechanisms for application state maintenance are less well developed. We discuss three different models to solve the problem and compare the advantages and disadvantages of each. Experimental results show that which model to use depends on application requirements. D-Stampede.NET is a platform supporting the development of applications that involve large time-sequenced data communication among heterogeneous clients. We describe our Web service implementation along with our state server solution to the application state management problem. A simple demonstration application is described and measured to validate performance.